Channel switching between television channels as being received by a television receiver (such as a television, a set-top box, . . . ) usually takes a certain amount of time, typically between 1.5 and 2 seconds, depending on the signal strength and reception hardware/software. During this switch time the video is usually black (blanked) and the audio is silent.
In normal situations, where the viewer triggers the channel switch (e.g., by pressing channel up/down buttons on the remote control), this period of silence/blackness is no problem since it is expected by the viewer, and also because the television programs that are being switched between have no relation between each other (are independent). In such a situation it is still desirable, however, to reduce the switch time (which is defined here as the time between presentation of the last video/audio from one (source) channel and the presentation of the first video/audio front the channel that is switched to).
In situations where the channel switch is made autonomously by the television receiver, for example because the presentation of one program is temporarily continued on another channel it is more important that the switch time is as short as possible, since the switch disrupts the flow of the presentation and the viewer's experience since (s)he does not expect a switch to happen. An example of such a situation is described in the Visible World patent application “System and Method for Simultaneous Broadcast for Personalized Messages”, filed on Apr. 24, 2001 with application Ser. No. 09/841,465 and is incorporated hereto by reference, which describes how to implement personalized messaging in a broadcast environment in a highly bandwidth efficient manner by using modular (slot-based) messages. In one embodiment, personalized messages are concentrated in one (or a few) dedicated digital streams, so that existing analog and digital television channels can “share” personalized messages by switching to and from these dedicated channels at the appropriate times. This leads to a highly bandwidth efficient system since the personalized messages are time-shared on one (or a few) channels.
The present invention describes methods for reducing the channel switch time from an analog or digital channel to a digital channel, and back.
Note that the related Visible World patent application “System and Method for Seamless Switching”, filed on Dec. 13, 2000 with application Ser. No. 09/735,983 and incorporated herein by reference, explains how to seamlessly switch between content elements (modules of personalized messages) within a digital stream. The present application discloses methods on how to seamless switch to such a digital stream from another analog or digital stream and back.